Diamond sifting Goby missing tail!

[JohnnyMartinez]

So my diamond sifting Goby had been doing wonderful for weeks, then all of a sudden I see it today, and his WHOLE tail is gone??? I tried to target feed him but he won't take the food, I have a yellow tang, foxface, 2 Clowns, purple dotty back, and a banggai Cardinal. Along with some snails few hermits and a green emerald crab, any idea what this could be???

 

[JohnnyMartinez]

Here is another picture with the lights on, this a 75 gallon reef tank btw

 

[crawling junk]

Emerald crabs are known for going after fish

 

[snorvich]

Emerald crabs are known for going after fish

True. And purple dottybacks, especially in small tanks, are terrors.